Abstract: A novel method and apparatus for photometrically analyzing a dilute solution containing chlorine dioxide is provided. The method includes introducing a sample flow into a conduit of a chlorine dioxide analyzer. At least one light emitting diode, in communication with the sample flow, is turned on and off to pass a light beam through the sample. Upon passing through the light beam through the sample the unabsorbed light is received onto a beam splitter which separates the light into a transmitted and a reflected light. The transmitted light is directed through a filter to a first detector which measures the low concentration chlorine dioxide and the reflected light is directed to a second detector which measures a high concentration of chlorine dioxide.